1. Field of the Invention
The present invention relates to a starter of an engine, and particularly to a starter of an engine having an automatic stopping device for the starter.
2. Discussion of Background
Formerly, a starter of an engine is composed of the starting motor 1, the electromagnetic switch 2, and the key switch 3 of a vehicle as shown in FIG. 3. The electromagnetic switch 2 is composed of two fixed contacts 2a and 2b, the moving contact 2c which opens and closes the fixed contacts 2a and 2b, the plunger 2d, which supports the moving contact 2c, and two coils 2e and 2f which draws the plunger 2d whereby the fixed contacts 2a and 2b are closed by the moving contacts 2c, or extinguish a drawing force applied on the plunger 2d. In this electromagnetic switch 2, the fixed contact 2a is connected to the battery 4 mounted on the vehicle, which is a power source, and the fixed contact 2b is connected to the starting motor 1. A terminal of the coil 2e is connected to the fixed contact 2b and another terminal of the coil 2e, to a contact point of the key switch 3, and a terminal of the coil 2f is connected to a contact point of the key switch 3 and another terminal of the coil 2f, to the earth.
The operation of the this conventional starter of an engine will be briefly explained.
When the key switch 3 is closed for starting up the engine, current flows in both coils 2e and 2f of the electromagnetic switch 2, by which the plunger 2d is drawn since the directions of winding of both coils 2e and 2f are the same and the magnetic fields produced by both coils are in the same direction, and finally the moving contact 2c shorts the fixed contacts 2a and 2b. When the fixed contacts 2a and 2b are closed, electric potentials at the both ends of the coil 2e are almost the same. Therefore current is not flown in the coil 2e and current is flown only in the coil 2f, which maintains the plunger 2d in a drawn state. In the mean time, when the starting motor 1 is driven and the engine starts up, the key switch 3 is opened. Then, current is flowing (in a reverse direction) from the fixed contact 2b to the coil 2e and the coil 2f. As a result, the magnetic fields produced by the coil 2e and the coil 2f are cancelled and the drawing force on the plunger 2e is lost. The plunger 2d is pushed back by a return spring, the moving contact 2c returns to the original positions, the fixed contacts 2a and 2b are opened, and the operation of the starting motor 1 is stopped.
However, in the above mentioned conventional starter of the engine, it is necessary that when the engine is to be started, the key switch 3 is kept closed, the ignition of the engine is judged by a driver according to a starting sound etc., and the key switch 3 is returned to the original positions. This operation is difficult especially for a beginner. Sometimes the engine is difficult to be started up since the driver is not accustomed to the operation of the key switch 3, and sometimes the driver keeps switching the key switch 3 inspite that the engine is already started, which destructs an overrunning clutch of the starting motor 1.